The time it takes for cactus seeds to germinate depends upon the type of cactus and the temperature. The seeds need no pre-treatment, just sprinkle them on some moistened seed starting mix and barely cover with fine sand. Place the tray inside a plastic bag and put it in a warm place (65F - 75F degrees). The seeds can take one week to several months to germinate. When they sprout remove the plastic bag and put the tray in a brightly lit place. If you start now, you should have a nice collection of baby cacti by late October.